<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
    var arr = [5, 6, 7, 8, 9, 10, 11, 12]
    function foo () {
    let i = 2
    for (; i < arr.length; i++) {
        // console.log(arr[i])		
        
        if (arr[i] % 3 == 0 || arr[i] % 5 == 0) {
            return i	
        }
    }
}
var res = foo()
console.log(res)
  </script>
</body>
</html>